Quinidine elimination in patients with congestive heart failure or poor renal function

Assessment of Quinidine-Induced Torsades de Pointes Risks Using a Whole-Body Physiologically Based Pharmacokinetic Model Linked to Cardiac Ionic Current Inhibition

The lethality of torsades de pointes (TdP) by drugs is one of main reasons that some drugs were withdrawn from the market. In order to assess drug-induced TdP risks, a model of cardiac ionic current suppression in human ventricular myocytes (ToR-ORd model), combined with the maximum effective free therapeutic plasma concentration or the maximum effective free therapeutic myocyte concentration was often used, with the latter proved to be more relevant and more accurate. We aimed to develop a whole-body physiologically-based pharmacokinetic (PBPK) model, incorporated with a human cardiomyocyte pharmacodynamic (PD) model, to provide a comprehensive assessment of drug-induced TdP risks in normal and specific scenarios. Quinidine served as an example to validate the PBPK-PD model via predicting plasma quinidine concentrations and quinidine-induced changes in QT interval (ΔQTc). The predicted plasma quinidine concentrations and ΔQTc values following oral administration or intravenous administration of quinidine were comparable to clinic observations. Visual predictive checks showed that most of the observed plasma concentrations and ΔQTc values fell within the 5th and 95th percentiles of simulations. The validated PBPK-PD model was further applied to assess the TdP risks using frequencies of early afterdepolarization and long-QT syndrome occurrence in 4 scenarios, such as therapeutic dose, supra-therapeutic dose, alkalosis, and hyperkalemia in 200 human subjects. In conclusion, the developed PBPK-PD model may be applied to predict the quinidine pharmacokinetics and quinidine-induced TdP risks in healthy subjects, but also simulate quinidine-induced TdP risks under disease conditions, such as hypokalemia and alkalosis.

The influence of heart failure on the pharmacokinetics of cardiovascular and non-cardiovascular drugs: a critical appraisal of the evidence

Prescribing in heart failure (HF), a common disease state that predominantly affects the older population, is often a challenging task because of the dynamic nature of the condition, requiring frequent monitoring and medication review, the presence of various comorbidities, and the frailty phenotype of many patients. The significant alterations in various organs and tissues occurring in HF, particularly the reduced cardiac output with peripheral hypoperfusion and the structural and functional changes of the gastrointestinal tract, liver and kidney, might affect the pharmacokinetics of several drugs. This review critically appraises the results of published studies investigating the pharmacokinetics of currently marketed cardiovascular and selected non-cardiovascular drugs in HF patients and control groups, identifies gaps in the current knowledge, and suggests avenues for future research in this complex patient population.

Correlation between plasma quinidine and cardiac effect

1 The relationship between serum quinidine levels and rate-corrected QT (QTc) interval after administration of single identical doses of quinidine was assessed. Quinidine concentrations were determined by a modification of Hamfelt & Malers' (1963) method. The significance and clinical application of our findings is discussed. 2 Individual responses (both in quinidine concentration and QTc prolongation) were variable, though the variation was no greater with QTc prolongation response than with serum quinidine levels. A significant peak in QTc prolongation occurred after quinidine administration and this was not accompanied by a similar peak in quinidine levels. There was some correlation (r = 0.53) between serum quinidine levels and QTc interval but a better correlation was found between rate of rise of quinidine concentration and QTc prolongation (r = 0.87). 3 One individual showed marked QTc prolongation with slow rate of rise of quinidine levels. Red cell quinidine levels were lower in this individual and he may be showing increased myocardial sensitivity to quinidine.

Effects of Quinine, Quinidine, and Chloroquine on α9α10 Nicotinic Cholinergic Receptors

In this study, we report the effects of the quinoline derivatives quinine, its optical isomer quinidine, and chloroquine on alpha9alpha10-containing nicotinic acetylcholine receptors (nAChRs). The compounds blocked acetylcholine (ACh)-evoked responses in alpha9alpha10-injected Xenopus laevis oocytes in a concentration-dependent manner, with a rank order of potency of chloroquine (IC50 = 0.39 microM) > quinine (IC50 = 0.97 microM) approximately quinidine (IC50= 1.37 microM). Moreover, chloroquine blocked ACh-evoked responses on rat cochlear inner hair cells with an IC50 value of 0.13 microM, which is within the same range as that observed for recombinant receptors. Block by chloroquine was purely competitive, whereas quinine inhibited ACh currents in a mixed competitive and noncompetitive manner. The competitive nature of the blockage produced by the three compounds was confirmed by equilibrium binding experiments using [3H]methyllycaconitine. Binding affinities (Ki values) were 2.3, 5.5, and 13.0 microM for chloroquine, quinine, and quinidine, respectively. Block by quinine was found to be only slightly voltage-dependent, thus precluding open-channel block as the main mechanism of interaction of quinine with alpha9alpha10 nAChRs. The present results add to the pharmacological characterization of alpha9alpha10-containing nicotinic receptors and indicate that the efferent olivocochlear system that innervates the cochlear hair cells is a target of these ototoxic antimalarial compounds.

Interactions between grapefruit juice and cardiovascular drugs

Grapefruit juice can alter oral drug pharmacokinetics by different mechanisms. Irreversible inactivation of intestinal cytochrome P450 (CYP) 3A4 is produced by commercial grapefruit juice given as a single normal amount (e.g. 200-300 mL) or by whole fresh fruit segments. As a result, presystemic metabolism is reduced and oral drug bioavailability increased. Enhanced oral drug bioavailability can occur 24 hours after juice consumption. Inhibition of P-glycoprotein (P-gp) is a possible mechanism that increases oral drug bioavailability by reducing intestinal and/or hepatic efflux transport. Recently, inhibition of organic anion transporting polypeptides by grapefruit juice was observed in vitro; intestinal uptake transport appeared decreased as oral drug bioavailability was reduced. Numerous medications used in the prevention or treatment of coronary artery disease and its complications have been observed or are predicted to interact with grapefruit juice. Such interactions may increase the risk of rhabdomyolysis when dyslipidemia is treated with the HMG-CoA reductase inhibitors atorvastatin, lovastatin, or simvastatin. Potential alternative agents are pravastatin, fluvastatin, or rosuvastatin. Such interactions might also cause excessive vasodilatation when hypertension is managed with the dihydropyridines felodipine, nicardipine, nifedipine, nisoldipine, or nitrendipine. An alternative agent could be amlodipine. In contrast, the therapeutic effect of the angiotensin II type 1 receptor antagonist losartan may be reduced by grapefruit juice. Grapefruit juice interacting with the antidiabetic agent repaglinide may cause hypoglycemia, and interaction with the appetite suppressant sibutramine may cause elevated BP and HR. In angina pectoris, administration of grapefruit juice could result in atrioventricular conduction disorders with verapamil or attenuated antiplatelet activity with clopidrogel. Grapefruit juice may enhance drug toxicity for antiarrhythmic agents such as amiodarone, quinidine, disopyramide, or propafenone, and for the congestive heart failure drug, carvediol. Some drugs for the treatment of peripheral or central vascular disease also have the potential to interact with grapefruit juice. Interaction with sildenafil, tadalafil, or vardenafil for erectile dysfunction, may cause serious systemic vasodilatation especially when combined with a nitrate. Interaction between ergotamine for migraine and grapefruit juice may cause gangrene or stroke. In stroke, interaction with nimodipine may cause systemic hypotension. If a drug has low inherent oral bioavailability from presystemic metabolism by CYP3A4 or efflux transport by P-gp and the potential to produce serious overdose toxicity, avoidance of grapefruit juice entirely during pharmacotherapy appears mandatory. Although altered drug response is variable among individuals, the outcome is difficult to predict and avoiding the combination will guarantee toxicity is prevented. The elderly are at particular risk, as they are often prescribed medications and frequently consume grapefruit juice.

Modulation by dietary salt of verapamil disposition in humans

BACKGROUND

The intestine is an increasingly well-recognized site of first-pass drug metabolism. In this study, we determined the influence of dietary salt on the steady-state disposition of verapamil, a drug that undergoes extensive first-pass metabolism.

METHODS AND RESULTS

Eight normal volunteers received 120 mg of racemic verapamil orally twice a day for 21 days. The disposition kinetics of verapamil enantiomers were determined after coadministration of intravenous deuterated verapamil with the morning oral dose on days 7, 14, and 21. Each study day was preceded by 7 days on a fixed-salt diet: in 5 subjects, the initial study was conducted during a low-salt (10 mEq/d) diet, the second study during a high-salt (400 mEq/d) diet, and the third during a low-salt diet, whereas in the other 3 subjects, the sequence of diets was reversed. Plasma concentrations of both unlabeled enantiomers (ie, from oral therapy) were significantly (P<0.05) lower during the high-salt phase (eg, mean area under the time-concentration curve [0 to 12 hours] for S-verapamil: 7765+/-2591 ng. min. mL-1 [high salt] versus 12 514+/-3527 ng. min. mL-1 [low salt], P<0.05). Peak plasma concentrations were significantly lower and the extent of PR interval prolongation significantly blunted with the high-salt diet. In contrast, data with labeled drug (ie, reflecting the intravenous route) were nearly identical for the 2 diets.

CONCLUSIONS

These data indicate that a clinically important component of presystemic drug disposition occurs at the prehepatic (presumably intestinal) level and is sensitive to dietary salt.

Effects of cardiovascular drugs on ATPase activity of P-glycoprotein in plasma membranes and in purified reconstituted form

Drug interactions with P-glycoprotein (Pgp) were quantitatively assessed using ATPase assay. Two experimental systems were used, (i) plasma membranes isolated from a multidrug-resistant cell line, which contained 30% Pgp as fraction of total membrane protein, and (ii) purified reconstituted Pgp. The cardioactive drugs verapamil, quinidine, diltiazem, nifedipine, and a series of digitalis analogs, interacted directly with Pgp as shown on ATPase in both systems. Apparent affinities of drug binding were calculated. Direct competition was shown between digitoxin and verapamil. Drug-drug interaction in vivo at the level of Pgp is expected from the results. This approach seems well-suited for empirical determination of drug interactions with Pgp, and prediction of drug-drug interactions.

Dietary salt increases first-pass elimination of oral quinidine

BACKGROUND

Some cytochrome P450 (CYP) enzymes, including CYP3A, are expressed not only in the liver but also in the intestine; the latter may therefore be an important site of drug disposition. Animal data suggests that dietary salt modulates expression of renal CYPs. We therefore hypothesized that intestinal CYP3A may be similarly modulated by dietary salt.

METHODS

The effect of changes in dietary salt on the disposition of two CYP3A substrates, quinidine (administered orally and intravenously) and 14C-erythromycin (administered intravenously) were determined after normal volunteers were given high-salt (400 mEq/day) and low-salt (10 mEq/day) diets for 7 to 10 days each.

RESULTS

Plasma concentrations after oral quinidine were significantly lower during the high-salt phase, with the difference between the two treatments attributable to changes within the first 1 to 4 hours after administration. For example, the area under the plasma concentration-time curve for the first hour after drug administration was 0.56 +/- 0.38 microgram.hr/ml for the high-salt diet compared with 1.57 +/- 0.60 micrograms.hr/ml for the low-salt diet (p < 0.05). Similarly, the peak plasma concentration (Cmax) achieved was lower and the time to reach Cmax was later for the high-salt diet (p < 0.05). In contrast, the terminal phase elimination half-lives were similar for the two diets, and no differences in disposition were found with the intravenous drug. The erythromycin breath test was unaffected by the dietary treatments.

CONCLUSIONS

These results indicate an effect of dietary salt on the presystemic disposition of orally administered quinidine. Although the mechanism(s) of CYP3A activity modulation is unknown, this finding may be important in determining drug availability in conditions associated with abnormal salt homeostasis.

Effect of grapefruit juice on the pharmacokinetics and pharmacodynamics of quinidine in healthy volunteers

A study was conducted to examine the effect of grapefruit juice on the disposition of quinidine sulfate and changes of QT intervals after oral administration to twelve healthy male volunteers. Participants received two oral doses of quinidine sulfate tablets (400 mg) with 240 mL of water or grapefruit juice, each separated by a 1-week washout period. Plasma samples for analysis of quinidine and its major metabolite, 3-hydroxyquinidine, were collected for a 24-hour period and analyzed by a high-performance liquid chromatography method. For pharmacodynamic data, the electrocardiograms (ECGs) were performed for 12 hours, and the recordings were marked for ECG interval at all blood collection time periods. There was no significant difference in pharmacokinetic parameters of quinidine when administered with grapefruit juice or water, except for time to maximum concentration (tmax), which was 1.6 hours after administration with water and 3.3 hours after administration with grapefruit juice. Administration with grapefruit juice also resulted in a 33% decrease in the area under the concentration-time curve (AUC) of 3-hydroxyquinidine compared with water, but did not increase the AUC of quinidine or change the ratio of AUC of 3-hydroxyquinidine to the AUC of quinidine. Pharmacodynamic parameters, including changes in the rate-corrected QT (QTc) interval, closely paralleled the pharmacokinetic data, in that administration with grapefruit juice led to delayed maximal effect on QTc and reduction in maximal effect. Administration with grapefruit juice therefore delays the absorption of quinidine and inhibits the metabolism of quinidine to 3-hydroxyquinidine.

Effects of the quinoline derivatives quinine, quinidine, and chloroquine on neuromuscular transmission

The quinoline derivatives quinine, its stereoisomer quinidine, and chloroquine may worsen or provoke disorders of neuromuscular transmission. In this study, we investigate effects of these drugs on neuromuscular transmission by conventional microelectrode as well as patch-clamp techniques. At 5 x 10(-5) M, quinine, quinidine, and chloroquine reduced the quantal content of the end-plate potential by 37-45%. Between 10(-6) and 10(-4) M, all 3 drugs progressively decreased the amplitude and decay time constant of miniature end-plate potential (MEPP) and miniature end-plate current (MEPC); at 5 x 10(-3) M, the MEPP became undetectable. The effect on the MEPP was not reversed by 1 microgram/mL neostigmine. Single-channel patch-clamp analysis of the effects of quinine showed that this agent causes a long-lived open-channel as well as a closed-channel block of AChR. Tests for competitive inhibition or desensitization of the acetylcholine receptor (AChR) by quinine in concentrations that had a marked effect on the MEPC and on single-channel open and closed intervals were negative. Because quinoline drugs adversely affect both presynaptic and postsynaptic aspects of neuromuscular transmission at concentrations close to those employed in clinical practice, they should not be used, or used with caution, in disorders that compromise the safety margin of neuromuscular transmission.

Effect of quinidine on kidney biochemistry and function in male Sprague-Dawley rats

Accumulation of the organic anion p-amino hippurate (PAH) and the organic cation tetraethyl ammonium (TEA) was decreased in renal cortical slices incubated with medium containing quinidine. Renal cortical slice oxygen consumption was also decreased. Quinidine reduced respiratory control index (RCI) and ADP/O ratio in isolated kidney cortex mitochondria. The in vitro data suggest that quinidine can alter renal transport and mitochondrial functions. Intraperitoneal administration of quinidine at 75 mg/kg twice a day for four days inhibited PAH and TEA transport in renal cortical slices. Renal cortical slice oxygen consumption was significantly decreased. Mitochondria showed a significant reduction in ADP/O ratio but no effect on RCI. Serum biochemical measurements indicated significantly elevated blood urea nitrogen. The data suggest that quinidine produces adverse renal effects in vitro and at high doses it produces nephrotoxic effects in vivo.

Efficacy of class 1C antiarrhythmic agents in patients with inducible ventricular tachycardia refractory to therapy with class 1A antiarrhythmic drugs

The efficacy of class 1C antiarrhythmic agents was determined in 36 patients with inducible sustained monomorphic ventricular tachycardia during baseline electrophysiology study (EPS), who continued to have inducible monomorphic ventricular tachycardia during EPS on class 1A antiarrhythmic therapy. Of 12 patients who partially responded to class 1A drugs, 11 (91.7%) continued to have a partial response during EPS on class 1C therapy, whereas one patient did not respond. Of 24 nonresponders to class 1A therapy, 2 (8.3%) responded during EPS on class 1C therapy, 7 (29.2%) partially responded, and 15 (62.5%) did not respond. In the 24 nonresponders to class 1A therapy, 9 of 17 patients (53%) with left ventricular ejection fraction (EF) > or = 30% responded or partially responded to class 1C therapy, compared with none of 7 patients with EF < 30% (P < .05). The EPS on class 1C agents in patients who fail to respond to class 1A therapy may be warranted only in those with EF > or = 30%.

Hemodynamic and neurohormonal effects of quinidine in patients with severe left ventricular dysfunction secondary to coronary artery disease or idiopathic dilated cardiomyopathy

Quinidine causes vasodilation directly and by inhibition of adrenergic vasoconstriction, but it also exerts negative inotropic activity. Although this drug is often administered to patients with severe congestive heart failure, the net consequences of these opposing actions have not been evaluated in such patients. The hemodynamic and neurohormonal response to oral quinidine (600 mg) in 19 patients with severe chronic heart failure was therefore determined. Vasodilation was the predominant effect of quinidine, with reductions in mean arterial, left ventricular filling and right atrial pressures of -9% (confidence interval [CI] -5 to -13), -8% (CI -19 to 3), -15% (CI -26 to -4), respectively. The quinidine-induced vasodilation increased plasma norepinephrine and epinephrine concentrations by 44% (CI +17 to +72) and 47% (CI +2 to +91), respectively. No change in cardiac performance was noted, with the cardiac index slightly increased (+10%, CI +2 to +17) and stroke work index unchanged (0%, CI -11 to +11) after quinidine. Although the mean serum quinidine concentration was within the therapeutic range or lower in all patients, the serum quinidine concentration and the change in mean arterial pressure did correlate (r2 = 0.64). In conclusion, vasodilation is the predominant hemodynamic effect of oral quinidine in patients with congestive heart failure. However, potential adverse effects may be caused by consequent neurohormonal activation.

Practical optimisation of antiarrhythmic drug therapy using pharmacokinetic principles

The optimisation of antiarrhythmic drug therapy is dependent on the definitions and methods of short term efficacy testing and the characteristics of those drugs used for rhythm disturbances. The choice of an initial antiarrhythmic drug dosage is highly empirical, and will remain so until the measurement of free concentrations, enantiomeric fractions and genetic phenotyping becomes routine. However, the clinician can devise an efficient initial dosage for efficacy testing procedures based on pharmacokinetic principles and disposition variables in the literature. In this regard, a nomogram for commonly used agents and dosages was constructed and is offered as a guide to accomplish this goal. Verification of the accuracy and usefulness of this nomogram in a prospective manner in patients with symptomatic tachyarrhythmias is still required. On a long term basis, dosage regimens can be modified by the use of pharmacokinetic principles and patient-specific target concentrations, in accordance with the methods used to monitor arrhythmia recurrence and drug-related side effects.

Poisoning due to class IA antiarrhythmic drugs. Quinidine, procainamide and disopyramide

Quinidine, procainamide and disopyramide are antiarrhythmic drugs in the class 1A category. These drugs have a low toxic to therapeutic ratio, and their use is associated with a number of serious adverse effects during long term therapy and life-threatening sequelae following acute overdose. Class 1A agents inhibit the fast inward sodium current and decrease the maximum rate of rise and amplitude of the cardiac action potential. Prolonged Q-T interval and, to a lesser extent, QRS duration may be observed at therapeutic concentrations of quinidine. With increasing plasma concentrations, progressive depression of automaticity and conduction velocity occur. 'Quinidine syncope' (a transient loss of consciousness due to paroxysmal ventricular tachycardia, frequently of the torsade de pointes type) occurs with therapeutic dosing, often in the first few days of therapy. Extracardiac adverse effects of quinidine include potentially intolerable gastrointestinal effects and hypersensitivity reactions such as fever, rash, blood dyscrasias and hepatitis. Procainamide produces electrophysiological changes that are similar to those of quinidine, although Q-T interval prolongation with the former is less pronounced at therapeutic concentrations. Hypersensitivity reactions including fever, rash and (more seriously) agranulocytosis are associated with procainamide, and a frequent adverse effect requiring cessation of therapy is the development of systemic lupus erythematosus. Of the 3 drugs, disopyramide has the most pronounced negative inotropic effects, which are especially significant in patients with pre-existing left ventricular dysfunction. As with quinidine, unexpected 'disopyramide syncope' at therapeutic concentrations has been described. Anticholinergic side effects are common with this drug and may require cessation of therapy. Disopyramide therapy may unpredictably induce severe hypoglycaemia. Severe intoxication with the class 1A agents may result from acute accidental or intentional overdose, or from accumulation of the drugs during long term therapy. Acute overdose can result in severe disturbances of cardiac conduction and hypotension, frequently accompanied by central nervous system toxicity. Decreased renal function can cause significant accumulation of procainamide and its active metabolite acecainide (N-acetyl-procainamide), resulting in severe intoxication. Mild to moderate renal dysfunction is less likely to lead to quinidine or disopyramide intoxication, unless renal failure is severe or concurrent hepatic dysfunction is present. Management of acute intoxication with class 1A drugs includes gut decontamination with provision of respiratory support and treatment of seizures as needed. Hypertonic sodium bicarbonate, by antagonising the inhibitory effect of quinidine on sodium conductance, may reverse many or all manifestations of cardiovascular toxicity.(ABSTRACT TRUNCATED AT 400 WORDS)

Marked heterogeneity in the intrahepatic distribution of quinidine in rats: implications in pharmacokinetics

Approximately 20 to 24 samples (0.1-0.2 g each) were obtained from each of six isolated rat livers following steady-state infusion of quinidine. The concentrations of quinidine, analyzed by an HPLC method, were found to vary markedly within each lobe (up to approximately 52-fold) or between lobes (up to approximately 25-fold) from the same liver. The maximum intrahepatic concentration difference in the six livers studied was 208-fold. Implications of the present study in the determination of liver drug concentration, and of the partition coefficient between liver and venous drug concentration in physiological pharmacokinetic modeling, as well as in hepatic modeling, are discussed.

Comparison of assay procedures used to measure total and unbound concentrations of quinidine

Individualized quinidine dosing through the assessment of serum concentrations is warranted because of the wide variability observed in its pharmacokinetic behavior and its reported narrow therapeutic index. The free fraction of quinidine also varies widely. Thus the development of procedures that could be widely used to determine quinidine free concentrations would be highly desirable. It was the purpose of this study to evaluate several procedures available to determine total serum quinidine concentrations (rate nephelometry [ICS], homogenous enzyme immunoassay [EMIT], and high-performance liquid chromatography [HPLC]). Furthermore, in samples from 46 patients, equilibrium dialysis and ultrafiltration procedures were compared for their ability to estimate quinidine free fraction. Finally, unbound concentrations of quinidine were compared using a modified EMIT procedure and a standard HPLC method to quantitate quinidine in ultrafiltrates from patient samples. For the measurement of total quinidine concentrations, reasonable agreement was seen when EMIT and ICS systems were compared with HPLC (ICS = 1.03.HPLC + 0.96, r = 0.93; EMIT = 1.08.HPLC + 0.38, r = 0.93) The mean errors, however, for these procedures were high (ICS +70 percent, range +7 to +233 percent; EMIT +35 percent, range 0 to 110 percent). Quinidine free fractions (QFF) determined by equilibrium dialysis (E) and ultrafiltration (U) showed good agreement (QFF(U) = 1.11.QFF(E) +0.0; r = 0.96). Unbound quinidine concentration determined by EMIT analysis of ultrafiltrate substantially overestimated the values obtained by HPLC analysis (mean error by EMIT 104 +/- 59 percent). It is concluded that HPLC is the method of choice for determining both total and unbound serum quinidine concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of cardiovascular disease on pharmacokinetics

The pathophysiologic changes occurring in cardiovascular disease can affect the kinetics of drugs in several different ways. The present review examines these modifications and the underlying mechanisms. The kinetics of specific agents, such as antiarrhythmic, antihypertensive, cardiotonic, and other drugs are considered, and the clinical implications are outlined. The clinician should be aware of these modifications, because they require an adjustment of the dosage regimen. A rational basis for a correct therapeutic choice can be provided by adequate knowledge of these modifications.

The clinical implication of changing unbound quinidine levels

Pharmacodynamic and pharmacokinetic aspects pertinent to the potential clinical application of unbound quinidine levels were studied. Following heparin administration during electrophysiologic testing in 10 patients receiving quinidine, there were significant increases in the mean (+/- SD) right ventricular effective refractory period (266 +/- 24 versus 279 +/- 23; p less than 0.025), free fatty acid concentration (515 +/- 213 versus 1071 +/- 359 mmol/L; p less than 0.001), and unbound quinidine concentration (0.3 +/- 0.1 to 0.6 +/- 0.1 microgram/ml; p less than 0.001) but no changes in heart rate, corrected QT interval, or total plasma quinidine concentration. Ten control patients showed no change in the right ventricular effective refractory period following heparin administration. These findings were consistent with a heparin-induced increase in unbound drug concentration and activity that was limited to the vascular compartment. Eleven patients studied on day 3 (+/- 1) and day 10 (+/- 3) during an acute myocardial infarction showed a significant decrease in unbound quinidine fraction (12 +/- 4% versus 9 +/- 4%; p less than 0.02) accompanied by a decrease, rather than the predicted increase, in half-life (7.1 +/- 2.7 versus 6.3 +/- 2.1 hours; p less than 0.02). Volumes of distribution remained stable while the mean quinidine clearance tended to increase. Half-life correlated with albumin changes (r = -0.71; p less than 0.02). Apparently, improvement in clinical status (assumed) and drug clearance (measured) negated the direct effects of the decrease in unbound quinidine fraction. Although unbound drug concentrations should correlate best with drug dynamic and kinetic information, full knowledge of the clinical context of such measurements is needed for appropriate interpretation.

Quinidine: an update on therapeutics, pharmacokinetics and serum concentration monitoring

After 70 years of regular use, quinidine remains one of the most useful drugs in the management of both supraventricular and ventricular arrhythmias. Quinidine sulfate, from conventional dosage forms, is absorbed rapidly and reaches peak levels in 1 hour. Sustained-release quinidine sulfate and gluconate are absorbed more slowly and, thus, may provide a more satisfactory response with less fluctuation in the peak and trough at quinidine concentrations. The half-life and absorption characteristics of sustained-release quinidine suggest that an 8- to 12-hour dosage regimen will produce smooth, sustained quinidine levels. Whereas quinidine and digitalis have been used concomitantly for years, dramatic elevations in blood digoxin levels have been observed. When quinidine is added to the regimen of a patient taking digitalis, these increased digoxin levels may be responsible for some of the adverse effects previously attributed to quinidine administration and can be reduced by adjustment of the digoxin dosage. Drug monitoring of serum quinidine concentrations as well as peak levels is essential to assess patient compliance and to determine that therapeutic levels are maintained. This is especially important because of the drug's relatively narrow therapeutic index and the changes in clearance that can result from drug interactions and renal and hepatic disturbances. A personal computer program is available to carry out pharmacokinetic calculations and assist in determining appropriate doses for individual patients.

Clinical pharmacokinetics in heart failure. An updated review

Pharmacokinetics is the study of the effect that the body has on drug absorption, distribution, metabolism and excretion. The pharmacokinetics of a specific drug are assessed by the volume of distribution, bioavailability, clearance and elimination half-life. Elimination half-life is directly related to the volume of distribution and inversely related to clearance. Any 1 or more of these parameters may be altered by physiological changes such as ageing, or disease states such as congestive heart failure. Congestive heart failure is associated with hypoperfusion to various organs including the sites of drug clearance, i.e. the liver and kidneys. It also leads to organ congestion as seen in the liver and gut. The main changes in drug pharmacokinetics seen in congestive heart failure are a reduction in the volume of distribution and impairment of clearance. The change in elimination half-life consequently depends on whether both clearance and the apparent volume of distribution change, and the extent of that change. Pharmacokinetic changes are not always predictable in congestive heart failure, but it seems that the net effect of reduction in the volume of distribution and impairment of clearance is that plasma concentrations of drugs are usually higher in patients with congestive heart failure than in healthy subjects. The changes in pharmacokinetics assume importance only in the case of drugs with a narrow therapeutic ratio (e.g. digoxin) and some of the antiarrhythmics such as lignocaine (lidocaine), procainamide and disopyramide. This necessitates reduction in both the loading and maintenance doses. Prolongation of the elimination half-life leads to delay in reaching steady-state, and therefore dose increments must be made more gradually. Plasma concentration measurements of the drugs concerned are a good guide to therapy and help to avoid toxicity. Pharmacokinetic changes are of less importance in the case of drugs with immediate clinical response, e.g. diuretics and intravenous vasodilators such as nitrates and phosphodiesterase inhibitors. The dose in the latter group can be titrated to the desired effect. Not all adverse reactions to drugs that may occur in heart failure are the result of alterations in pharmacokinetics; rather, some may be due to important drug interactions. An interaction may occur directly e.g. reduction of renal clearance of digoxin by captopril and quinidine; or indirectly, e.g. through diuretic-induced hypokalaemia, which exacerbate arrhythmias associated with digoxin and antiarrhythmics such as quinidine and procainamide.

Tocainide plus quinidine for treatment of ventricular arrhythmias

Tocainide and quinidine were administered both as single agents and in combination to 14 patients with chronic ventricular arrhythmias. Therapy with tocainide was limited by the occurrence of dose-related adverse reactions in 8 patients, but could be titrated to a dose that was well-tolerated in 13 of 14 and effective in 2 of 13. The addition of quinidine gluconate to the tolerated dose of tocainide increased the number of patients with arrhythmia suppression from 2 to 6. After tocainide washout, quinidine alone suppressed arrhythmias in only 3 patients. Analysis of electrocardiogram intervals showed that the drugs had additive effects on the coupling interval of the sinus beat to the predominant ectopic beat, but exerted antagonistic effects on the corrected QT interval. These findings suggest that the combination may be clinically useful, exerting pharmacologic effects unlike either agent alone.

Chronic ventricular arrhythmias: which drug for which patient?

Many agents, including a number of drugs recently approved by the Food and Drug Administration, are now available for the treatment of chronic ventricular arrhythmias. The so-called first-generation agents--quinidine, procainamide and disopyramide--have been used in large numbers of patients for many years, and the safety and efficacy profiles of these drugs are well established. The "second-generation" antiarrhythmic agents recently approved by the Food and Drug Administration offer promising new alternatives; however, their safety and efficacy profiles have yet to be confirmed for broad populations over extended periods of time. Although it is recognized that the choice of agent for treatment of a particular patient is a "therapeutic trial," with an unpredictable outcome of efficacy and adverse effects, certain "descriptors," such as patient age or co-existing medical conditions, are often helpful in determining which agent is most likely to be clinically effective, and which agents are most likely to produce adverse effects. When other medical conditions such as hepatic or renal failure are present, the appropriate choice of drug and dosage is required for optimal management of the arrhythmia and for prevention of overdosage, exacerbation of other medical problems and deleterious interactions. Combination therapy with multiple antiarrhythmic agents is often quite effective for increasing arrhythmia control without increasing adverse effects. However dosage modifications are often necessary when an antiarrhythmic drug is given in conjunction with another such agent, or with agents that also have electrophysiologic activity or modify metabolic or elimination functions. The following report is one clinician's approach for optimizing efficacy and minimizing toxicity while using the difficult class of drugs called antiarrhythmic agents. It will encourage the use of certain drugs before others, based on considerations of efficacy, safety, ease of administration, follow-up, and other factors.

Procainamide pharmacokinetics in patients with acute myocardial infarction or congestive heart failure

Abnormal procainamide pharmacokinetics (prolonged half-life and decreased volume of distribution) and pharmacodynamics (decreased threshold for the suppression of premature ventricular complexes) have been suggested in patients with acute myocardial infarction or congestive heart failure, or both. To better define procainamide kinetics, 37 patients in the acute care setting received intravenous procainamide (25 mg/min, median dose 750 mg) with peak and hourly blood samples taken over 6 hours. Compared with the 10 control patients, the 12 patients with acute myocardial infarction and the 15 patients with congestive heart failure had normal procainamide pharmacokinetics with respect to half-life (2.3 +/- 1.0, 2.5 +/- 0.9 and 2.6 +/- 0.8 hours, respectively), volume of distribution (1.9 +/- 0.7, 1.8 +/- 0.4 and 1.8 +/- 0.5 liters/kg, respectively), clearance (11.3 +/- 7.5, 9.3 +/- 3.6 and 9.1 +/- 3.5 ml/min per kg, respectively) and unbound drug fraction (66 +/- 9, 66 +/- 9 and 69 +/- 4%, respectively). Low thresholds for greater than 85% premature ventricular complex suppression were confirmed in these patients (median 4.7 micrograms/ml in patients with acute myocardial infarction and 3.3 micrograms/ml in patients with congestive heart failure). Thus, differences in the response of premature ventricular complexes to procainamide reflect electropharmacologic differences dependent on clinical setting rather than pharmacokinetic abnormalities. Furthermore, the reduction of procainamide dosing in patients with acute myocardial infarction or congestive heart failure, based solely on prior kinetic data, may result in inappropriate antiarrhythmic therapy.

Ventricular arrhythmias in severe heart failure: incidence, significance, and effectiveness of antiarrhythmic therapy

Forty-three patients receiving maximal medical therapy for severe chronic heart failure from dilated cardiomyopathies (28 ischemic, 15 idiopathic) and ventricular premature beats (VPBs) on the 12-lead ECG had baseline 24-hour ambulatory ECG monitoring. Complex VPBs (multiform, repetitive--couplets, R on T phenomenon) and asymptomatic, nonsustained ventricular tachycardia were present in 38 patients (88%) and 22 patients (51%), respectively. Twenty-three patients (group I) were placed on long-term antiarrhythmic therapy (20 patients received procainamide and the remaining quinidine). Twenty patients (group II) did not receive antiarrhythmic therapy. At baseline, no significant differences between the two groups were noted for age, functional class, type of cardiomyopathy, medical therapy for heart failure, cardiothoracic ratio, radionuclide ejection fraction, or rate and complexity of the ventricular arrhythmias on the 24-hour ambulatory ECG tracings. At a mean follow-up period of 16 months (range 1 to 37), there were 16 deaths, 10 (62%) of which were sudden and unexpected. No significant differences in the incidence of sudden death and overall mortality were noted between the two groups. Among patients with nonsustained ventricular tachycardia, those who died suddenly had a lower mean left ventricular ejection fraction (0.15 +/- 0.01) when compared to the survivors (0.23 +/- 0.02; p less than 0.01). It is concluded that patients with severe heart failure have a high mortality from both sudden and nonsudden cardiac death, incidence of complex VPBs is very high, sudden death is more common when the left ventricular function is severely compromised, and apparently, therapeutic plasma levels of conventional antiarrhythmic drugs do not protect this group of patients from dying.

Quinidine is a competitive antagonist at alpha 1- and alpha 2-adrenergic receptors

Although quinidine is known to have antiadrenergic effects in the cardiovascular system, the precise mechanism by which it exerts these effects is not well defined. We asked whether quinidine binds directly to adrenergic receptors. Radioligand-binding assays were used to identify alpha 1-adrenergic receptors [( 3H]prazosin-binding sites) on membranes prepared from rat heart and kidney, alpha 2-adrenergic receptor [( 3H]yohimbine-binding sites) on human platelets and rat kidney membranes, and beta-adrenergic receptors [( 125I]iodocyanopindolol-binding sites) on rat heart and kidney membranes. Although it did not effectively compete for binding to beta-adrenergic receptors, quinidine competed for binding to alpha 1- and alpha 2-adrenergic receptors and yielded equilibrium dissociation constants of 0.3-3 microM. Two other antiarrhythmic agents, lidocaine and procainamide, did not compete for binding to alpha-adrenergic receptors. Further experiments demonstrated that the interactions of quinidine with the cardiac alpha 1- and platelet alpha 2-adrenergic receptors were competitive and reversible. We conclude that that antiadrenergic actions of quinidine can be explained by occupancy and competitive blockade of alpha 1- and alpha 2-adrenergic receptors.

Therapy with conventional antiarrhythmic drugs for ventricular arrhythmias

Conventional antiarrhythmic drugs are an important tool for the clinical cardiologist for the treatment of ventricular arrhythmias. Knowledge of the different properties of these drugs will help decrease the incidence of adverse effects and increase the frequency of successful therapy.

Factors affecting quinidine protein binding in humans

The free (unbound) concentration of drug in plasma is often an important determinant of pharmacological and toxicological effects. Unfortunately, studies examining the factors influencing the free fraction of quinidine in plasma have yielded inconsistent results. It is probable that differences in the type of blood collection tubes utilized and the analytical procedure employed biased some of these estimates of quinidine binding. The present study was executed in a manner free of factors now known to introduce artifacts into estimates of the free fraction of quinidine. In healthy volunteers, the free fraction of quinidine (1.0 microgram/mL) was 0.129 +/- 0.019 (mean +/- SD) and was constant throughout the therapeutic range. A high-affinity, low-capacity binding site (K = 1.17 X 10(5) M-1; nP = 3.49 X 10(-5) M) and a low-affinity, high-capacity binding site (K = 1.33 X 10(3) M-1; nP = 3.14 X 10(-3) M) were identified. The characteristics of quinidine binding in a 4.5-g/dL solution of human serum albumin (K = 3.05 X 10(3) M-1; nP = 1.36 X 10(-3) M) suggested that the low-affinity, high-capacity binding site was on this quinidine free fraction increased from 0.114 to 0.231. A lidocaine concentration of 250 micrograms/mL caused a similar increase. Patients suffering traumatic injury had a significant increase in alpha 1-acid glycoprotein concentration (197 mg/dL) and a decreased quinidine free fraction (0.075 +/- 0.019). Patients with hyperlipidemia had free fractions similar to those observed in healthy individuals (0.118 +/- 0.019).(ABSTRACT TRUNCATED AT 250 WORDS)

Selection of analytic methods for therapeutic drug monitoring

Selection of an analytic method for therapeutic drug monitoring usually involves an initial choice between chromatography and immunoassay. Once this decision has been made, numerous options remain within these two broad categories. There is no single correct or preferred assay technique. The best decision, based on technical, clinical, and economic considerations, will vary in different clinical and laboratory environments. The laboratory that has sufficient resources to maintain more than one type of technology will have a greater degree of flexibility in solving special problems.

Abnormal quinidine binding in survivors of prehospital cardiac arrest

Quinidine binding was studied in 15 survivors of prehospital cardiac arrest and was compared to 18 normal individuals and 20 patients with coronary artery disease. The unbound quinidine fraction was 6.3 +/- 2.8% in the survivors of prehospital cardiac arrest, a value significantly lower than normal individuals (unbound quinidine fraction = 9.9 +/- 3.0%, p less than 0.005). Furthermore, unbound quinidine fraction correlated with interdose quinidine half-life in the six survivors of prehospital cardiac arrest where this could be measured (r = 0.79, p less than 0.05). The resultant quinidine interdose half-life was significantly prolonged (10 +/- 3 hours) when compared to normal (6 +/- 2 hours, p less than 0.02). The reduction in free drug fraction in cardiac arrest survivors was a nonspecific finding in that free drug fraction was also reduced in the patients with coronary artery disease (unbound quinidine fraction = 7.4 +/- 3%) and was independent of the alpha-1-glycoprotein concentration. Therefore survivors of prehospital cardiac arrest have a mean 40% reduction in free quinidine drug fraction which results in less free drug at any given total drug concentration and may relate to quinidine pharmacokinetics and pharmacodynamics in this patient group.

Determination of quinidine in serum by spectrofluorometry, liquid chromatography and fluorescence scanning thin-layer chromatography

Quinidine is determined in serum by direct and extraction spectrofluorometry, by reflectance fluorescence scanning thin-layer chromatography (TLC), and by high-performance liquid chromatography (HPLC). Least-squares analyses of patients' sera (n = 62) analyzed first by direct fluorometry (x) and then HPLC (y) gave a slope of 0.52, an y-intercept of -0.40, a standard error of estimate of 0.65, and a correlation coefficient of 0.83. Comparison of patients' sera (n = 59) determined by extraction fluorometry (x) and then HPLC (y) gave a slope of 0.998, an y-intercept of -0.175, a standard error of estimate of 0.30, and a correlation coefficient of 0.96. Comparison of patients' sera (n = 36) by HPLC (x) and then reflectance fluorescence scanning TLC (y) gave a slope of 0.837, an y-intercept of 0.152, and a correlation coefficient of 0.94. Methaqualone and oxazepam interfere with HPLC. Within-run precision is 1.6, 1.0, 5.2 and 3.0% by direct fluorometry, extraction fluorometry, TLC and HPLC while between-run precision is 5, 3.5, 9 and 6.0%, respectively.

Effect of food and an antacid on quinidine bioavailability

Two 200 mg quinidine sulfate tablets were administered to nine healthy male subjects in the fasting state, immediately after a balanced meal, and with 30 ml of aluminum hydroxide gel using a complete crossover design. Serum and urine samples were taken over 32 and 60 h, respectively. Quinidine concentrations were measured using a high-performance liquid chromatography assay specific for quinidine. Computer fitting of the data to several models indicated that a one-compartment model with zero-order absorption and a lag time best fit all the data. Quinidine elimination and urine pH were unaffected by the study conditions. While the maximum serum concentration (Cmax) and area under the serum concentration-time curve (AUC) were unaffected by administration of quinidine with food or antacid, there was a 44 per cent increase (p less than 0.10) in time to Cmax (tmax) following quinidine administration with food. Thus, while the extent of quinidine absorption was unaffected by food or the antacid used, the rate of quinidine absorption was significantly reduced by food as reported earlier.